Shielded cathode ray tube electron gun

ABSTRACT

An improved electron gun structure is provided for use in a cathode ray tube wherein insulative shielding is arranged to substantially encompass at least a portion of the plural electrode arrangement of the gun assembly. Such shielding, being dimensioned to be spaced from the interior surface of the envelope neck portion, is suitably positioned and retained relative to the support rods of the gun structure in a manner that the shielded gun assembly is inserted as a unit into the envelope neck portion during tube fabrication.

United States Patent Kerr et al. 1 Nov. 6, 1973 SHIELDED CATHODE RAYTUBE 2,567,874 9 1951 Cage 313/313 x ELECTRON GUN 3,462,629 8/1969 Bell313/70 C X 2,569,654 10/1951 Cage 313/239 X [75] Inventors: Jacob E.Kerr; Joseph D. Reardon,

both of Seneca Falls Primary ExaminerJohn K. Corbin [73] Assignee: GTESylvania Incorporated, Seneca Attorney-Norman Y et 3L Falls, NY. 7 22Filed: May 25, 1972 [57] ABSTRACT An improved electron gun structure isprovided for use [21 1 Appl' 256642 in a cathode ray tube whereininsulative shielding is arranged to substantially encompass at least aportion of [52] U.S. Cl 313/70 C, 313/239, 313/313 the pl r l electrodearrang m n of the gun embly. [51] Int. Cl. H0lj 29 50 Such Shielding,being dimensioned to be spaced from [58] Field at Search 313/239, 241,313, the interior Surface of the envelope neck p is 313/70 R, 70 Csuitably positioned and retained relative to the support rods of the gunstructure in a manner that the shielded [56] References Cited gunassembly is inserted as a unit into the envelope UNITED STATES PATENTSneck portion during tube fabrication.

3,558,954 l/l97l Lilley 313/313 X 8 Claims, 6 Drawing FiguresPATENTEDNnv ems 3771.003

SHEET 20F 2 SHIELDED CATHODE RAY TUBE ELECTRON GUN BACKGROUND OF THEINVENTION This invention relates to cathode ray tube electron gunstructures and more particularly to an electron gun structureincorporating shielding means to provide improvedoperationalcharacteristics.

During the operation of cathode ray tubes, stray or uncontrolledelectron emission and undesired arcing or electrical leakage conditionssometimes develop within the electron gun structure, or in the immediateregion thereof. Such conditions not only cause annoying distractions,evidenced in the visual display of the tube, but may alsoproducedeleterious results to the tube per se and/or to the operating circuitryassociated therewith. The undesirable stray emission, arcing and leakagecircumstances result from a combination of factors that contribute invarying degrees. Such factors include extraneous projections within thegun structure resultant from electrode welding, the release of priorlyabsorbed gases from the gun structure during tube operation, themigration of gettering material, and the presence of minute foreignparticles. Of these factors an attempt to eliminate or minimize spuriouswelding projections is effected by improved welding procedures. Effortsto reduce the possible prevalence and release of unwanted gas from thegun and tube structure is made by employing refined degassing techniquesboth prior to and during tube processing. Due to the nature of the tubeenvelope, and the usually inherent structural contents thereof, theproblem of reducing and eliminating the prevalence of minute foreignparticles therein and the possiblemigration of gettering material has amore elusive solution. For example, the interior of the funnel portionand the upper portion of the neck region is normally coated with anelectrical conductive material that is sometimes prone to flake in tinyparticles. In addition, conventional aluminizing of the forward portionof the envelope may result in the occasional presence of loose bits ofaluminum within the envelope. In the usual procedure for fabricating acathode ray tube, the envelope portion is prepared wherein portions ofthe interior have been carbon coated, the screen suitably formed on theinterior of the viewing panel or other support medium, and the aluminumfilm disposed thereover as desired. The electron gun assembly, which issupported on a stem closure wafer having an exhaust tubulation therein,is inserted into the open neck portion of the envelope, whereupon thestem wafer is peripherally sealed to the open end of the envelope neck.During subsequent processing of the tube, gases from within the envelopeare evacuated via the exhaust tubulation. This exhaust procedure effectsan outgoing flow of gas and gas-borne particles past the electron gunstructure which makes this assembly particularly vulnerable to possibleresidual environmental contamina- OBJECTS AND SUMMARY OF THE INVENTIONIt is an objectof the invention to reduce the aforementioneddisadvantages and provide an improved cathode ray tube electron gunstructure that is less prone to stray emission, electrical leakage andarcing.

Another object is to provide an electron gun structure that hasprovisions for protecting at least some of the electrode areas fromenvironmental contaminants within the tube.

A further object is to provide a cathode ray tube hav ing improvedoperational characteristics.

The foregoing objects are achieved in one aspect of the invention by theprovision of an improvedcathode ray tube electron gun structure. A.group of sequentially associated electrodes are arranged to provide atleast one beam of electrons. A plurality of glass support rods arespatially oriented peripheral to the electrode arrangement to effectsupport and affixed positioning thereof. An insulative shielding meansis arranged in a substantially encompassing manner about at least aportion of the supported electrodes. The shielding is telescoped overthe gun structure in a manner to be po sitioned and retained relative tothe support rods to provide shieldings for the gun assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial plan view showingthe neck section and screen portions of a plural-gun color cathode raytube embodying the invention;

FIGS. 2 and 3 are sectional views of FIG. 1 taken along the plane 2-2thereof illustrating embodiments of the invention;

FIGS. 4 and 5 are sectional views oriented similarly to FIG. 2 butshowing embodiments of the invention related to a plural in-line gunstructure; and

FIG. 6 illustrates one means of shield attachment to a support rod.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding ofthe present invention, together with other and further objects,advantages and capabilities thereof, reference is made to the followingspecification and appended claims in connection with the aforedescribeddrawings.

With reference to FIG. 1, in describing one embodiment of the invention,there is shown pertinent portions of a typical three-gun color cathoderay tube 11 as employed in producing visual displays such as television.The neck portion 13 is suitably connected to an oppositely disposed facepanel portion 15 by an intermediate funnel portion of which only thehigh voltage connection area 17 is shown. Within the neck portion 13there is positioned an electron gun assembly 19 having three individualgun structures 21 of which only two are revealed in FIG. 1. The gunassembly embodiment as further delineated in FIGS. 1 and 2 is a deltaarrangement, but such is not to beconsidered limiting as the inventionis also applicable to single gun structures or other plural gunarrangements to be subsequently described herein. In the embodiment l9presently con sidered, each of the individual electron guns generates,forms and focuses a discrete beam of controlled electrons 23 whichtraverses the magnetic convergence assembly 25 terminally positioned onthe mount assembly. This convergence assembly imparts positionalcorrections to the beams 23 as are necessaryfor directing them inoptimum paths to achieve convergence at the plane of the aperture mask27. By this convergence, the individual beams 23 are positioned to passthrough the apertures 29 therein; whereupon they penetrate theusually-present reflective aluminum film 30 therebeneath, and thencethey impinge and excite the proper dot patterns 31 of thecathodoluminescent screen 33 disposed on the interior surface of theface panel 15. Each of the individual gun structures 21 of the electrongun assembly 19 is made up ofa sequential longitudinal arrangement ofrelated electrodes. For example, starting with the base or stem closureend 35 of the tube 11 the first or adjacent electrode is a cathodeassembly structure 37 which contains an indirectly heated cathode 39;sequentially positioned therefrom is a first or control grid 41, asecond grid 43, a third grid 45, and a fourth or terminal grid 47,respectively. Functionally, the cathode 39 generates a beam of electrons23 which is modulated by the control grid 41, initially accelerated bythe second grid 43, focused by the third grid 45, and imparted withfinal velocity by the terminal high voltage grid 47. Electricalconnection is made to all of the electrodes, except the terminal grid47, by a plurality of electrode connectors or leads 49 which are hermetically sealed in the stem closure base of the tube 35, wherein alsois evidenced the sealed exhaust tubulation 50. In the case of theterminal grid 47, electrical connection is made through a plurality ofresilient snubbers 51 which are peripherally affixed to the contiguousmagnetic convergence assembly 25. These snubbers serve to both axiallycenter the electron gun assembly 19in the neck portion 13 of the tubeand make high voltage electrical connection to the internal conductivecoating 53 lining the upper part of the neck portion 13 and extendingtherefrom over the interior surface of the funnel portion 16, a portionof which is shown. A high voltage connector means 55 is hermeticallysealed in the aforementioned funnel portion 16 to connect the internalconductive coating 53 to an external high voltage source 57. Therespective electrode arrangements of the individual guns 21, making upthe electron gun assembly 19, are affixed to and supported by aplurality of insulative glass support rods 59. For example, in theembodiment shown in FIGS. 1 and 2, an arrangement of three spatiallyrelated longitudinal support rods is employed.

. An insulative shielding means 63, formed for example of a glassmaterial, is arranged to substantially encompass at least a portion ofthe electron gun assembly 19. The shielding is spaced from the interiorsurface of the envelope neck portion 13 and located relative to thesupport rods 59 being telescoped or fitted longitudinally over the rodsand positioned by attachment means associated with at least one of therods. As shown in FIGS. 1 and 2, the glass shielding means 63 issubstantially cylindrical in shape and is affixed to one of the rods 59by attachment means 67 in the form of at least one area of bonding fritapplied therebetween. Attachment of the shielding sleeve 63 ispreferably effected on one rod to allow for possible differentialexpansions of the gun assembly 19 and the encompassing glass shielding63 that may result from the processing temperatures encountered duringtube fabrication. It is desired that the shielding be substantiallysnug-fitting on the support rods 59. To achieve this end and tocompensate for expansion differentials, a longitudinal slit 71 may beincorporated in the device as indicated in FIG. 2.

Another embodiment of the shielding means is illustrated in FIG. 3, theview of which is of similar orientation in the mount structure to thatdelineated in FIG. 2. The shielding means 75, in this instance, isformed of a plurality of curved glass leaves 77. As shown, threesubstantially similarly shaped leaves are positioned in a cooperatingmanner about the electron gun assembly 19 to collectively provide aperipheral encompassment of at least a portion of the gun structure.Reference is made to FIG. 6 wherein a type of leaf construction isfurther detailed. Each of the leaves 77 has two opposed substantiallyarcuate end-oriented edges 79 and 81, and two opposed substantiallystraight side-oriented edges 83 and 85, respectively. The three curvedleaves 77 are collectively arranged with the side edges being adjacentlypositioned in a lateral relationship to effect the encompassingshielding 75. In this embodiment, each of the curved leaves 77 isattached to a respective individual support rod 59. Appropriate modes ofattachment are, for example, areas of compatible high temperature glassfrit suitably disposed between adjacent surfaces of the leaf and thesupport rod. Another attachment means is evidenced in FIG. 6 wherein aplurality of locating pins 89 embedded in the support rod 59 projecttherefrom to mate with compatible apertures 91 in the shielding means.circumspect terminal swaging of the pin projecting beyond the shieldingsurface or the discrete application of a high temperature bonding fritto the pin-aperture region consummates attachment.

Additional embodiments of electron gun shielding are depicted in FIGS. 4and 5 wherein shielded in-line gun structures 93 are shown. These viewsare likewise oriented similar to that of FIG. 2. In FIG. 4, theshielding sleeve 95 is substantially rectangular in shape andencompasses an electron gun assembly 97 which in this instance utilizesfour similar support rods 99. Attachment of the shield 95 to the relatedsupport rods is effected to one of the rods by a suitable deposition offrit 101 or by the pin-aperture arrangement 89, 91 as illustrated inFIG. 6. As with the embodiment shown in FIG. 2, a longitudinal slit 103can be incorporated into the sleeve to facilitate aforedescribeddifferential expansion characteristics and effect close adherence of theshielding means to the gun assembly.

In FIG. 5, another form of plural-leaf type shieldin 105 is illustratedwherein formed leaves 107, 108, 109 and 110 are separately attached tothe individual support rods 99 as, for example, by frit 101 or by apinaperture arrangement 89,91.

THe glass materials associated with the electron gun and neck portionsof a color cathode ray tube, for example, have melting points well abovethe temperatures encountered during the processing, wherein the gunassembly 19 is discretely subjected to elevated temperatures, usually byinduction heating, to aid in degassing the elements comprising theassembly structure. The glass of the support rods 59, 55 is usually ahigh silica containing material having a softening point in theneighborhood of 820830 centigrade; while the glass composition of theneck portion 13 of the color tube 11, which is further removed from themetallic mass of the gun structure, is normally a high lead contentmaterial exhibiting a softening point in theregion of 630-640centigrade.

During tube processing, the glass support rods are subjected to heatthat is both conducted and radiated from the heated metallic electrodesof the gun assembly 19, and may, for example, reach temperature levelsin the region of 500 centigrade. Therefore, the processing temperaturesencountered by the shielding means peripherally contiguous to thesupport rods may be somewhere in the neighborhood of 450 centigrade.Thus, the glass material comprising the various embodiments of shieldingencompassments should have a softening point characteristic in excess of500 centigrade. In each structural embodiment it is preferred thatcompatible coefficients of thermal expansion to be evidenced for theglass material of the shielding means and for that of the support rods,to which the respective shielding is affixed, and also for the bondingfrit when such means of attachment is utilized.

After the basic rod-supported electrode assembly is carefullyconstructed in a manner to contain a minimum of contaminants, thescrupulously cleaned and substantially degassed shielding means areapplied and affixed to the gun assembly. The shielding may cover themost vulnerable portion or the whole of the gun assembly, as may bedesired. The shielded gun assemblies are then stored in a cleancontrolled environment until the time when they are inserted and sealedinto the tube. envelopes as part of the tube fabrication procedure. Itis also in keeping with the concept of the invention for the shieldingmeans to afford an additional advantage, wherein the composition of theglass material is of a nature to provide absorptive shielding ofspurious radiations which may, in certain instances, be projected fromthe electron gun. While the shielding means tends to minimize theentrance of the aforedescribed contaminant materials into the gunassembly, there is the possibility that some contaminants may be presenttherein before the shielding is applied thereto. ln the type of electrongun exemplified in FIG. 1, the fourth grid 47 operates at a much higherpotential than the third grid 45. Thus, if undesirable conditions arepresent in the gun structure, x-radiations are apt to emanate therefromin particularly the vicinity of grid three-grid four electrodes, suchradiations being primarily due to stray or field emission bombardment ofenvironmental contaminants and electrode surfaces in that region.Therefore, if radiation absorptive compounds are incorporated in theshielding glass composition, an additional advantage is achieved. Suchcontrolling constituents, in amounts necessary to achieve the degree ofdesired radiation shielding results, are in the form of at least onemetallic compound, an oxide for instance, selected from the groupconsisting essentially of lead, barium and strontium.

Thus, there is provided a shielded cathode ray tube electron gunstructure wherein conditions are less conducive for the generation ofstray emission, electrical leakage, arcing and the emanation of spuriousradiation. The shielding means. affords protection for the mountassembly from environmental contaminants, and as a result providesimproved operational characteristics.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilledin the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:

1. An improved electron gun structure for use in a color cathode raytube having an envelope formed of a neck portion, a funnel portion and aface panel portion whereupon a cathodoluminescent screen is disposed,said electron gun structure being constructed for subsequent orientationwithin the neck portion of said envelope and comprising:

a plurality of longitudinal arrangements of associated electrodesrelated in amanner to subsequently provide for generating, forming andfocusing a plurality of beams of electrons toward saidcathodoluminescent screen;

a plurality of glass support rods spatially oriented peripheral to saidelectrode arrangements to provide support and affixed positioning forsaid related electrodes in said gun structure;

a common magnetic convergence assembly contiguous to and extendingforward of the terminal electrodes of said gun structure, and havingresilient means peripherally associated therewith to effect the.subsequent centering of said electron gun structure in the neck portionof said envelope; and

insulative glass shielding means arranged in a substantiallyencompassing manner about said supported electrode arrangements, saidshielding beingdimensioned to be spaced from the interior surface ofsaid envelope neck portion when said gun is inserted therein to provideshielding for said electrodes, said glass shielding means beingpositioned and retained in contiguous bonded relationship to at leastone of said support rods in said gun structure, said shielding beingoriented immediately to the rear of said convergence assembly.

2. An electron gun structure according to claim 1 wherein saidinsulative shielding means is fitted longitudinally over the glasssupport rods and positioned by plural pin attachment meansassociatedwith at least one of said rods.

3. An electron gun structure for use in a color cathode ray tubeaccording to claim 1 wherein said insulative shielding means are in theform of a plurality of curved glass leaves whereof each has two opposedsubstantially arcuate end oriented edges and two opposed substantiallystraight side oriented edges, said side edges being adjacentlypositioned in a lateral relationship to collectively form a peripheralencompassment of the plural beam electron gun structure, each of saidleaves being attached to an individual of said support rods.

4. An electron gun structure for a color cathode ray tube according toclaim 1 wherein the composition of said insulative shielding glasscontains an x-radiation absorptive material in the form of at least onemetallic compound selected from the group consisting essentially oflead, barium and strontium.

5. A plural beam color cathode ray tube comprising:

an envelope having face panel, funnel and neck portions; g

a patterned catho'doluminescent screen disposed on the interior surfaceof said face panel;

a plural beam electron gun structure located within said envelope neckportion in a manner to project a plurality of electron beams toward saidpatterned screen, said gun structure being formed of a plurality ofsequential arrangementsof associated electrodes positionally related byseveral spatially oriented longitudinal glass support rods;

a common magnetic convergence assembly contiguous to and extendedforward of the terminal electrodes of said gun structure and havingresilient means peripherally associated therewith to center saidelectron gun structure in the neck portion of said envelope; and

insulative glass shielding means arranged in a substantiallyencompassing manner about said electron gun structure and spaced fromthe interior surface of said envelope neck portion to provide shieldingfor said electrodes, said shielding means being positioned and retainedin bonded attachment to said gun structure support rods immediately tothe rear of said convergence assembly.

6. A color cathode ray tube according to claim wherein said electron gunshielding means is in the form of a sleeve fitted longitudinally overthe glass support rods of said electron gun structure in a contiguousmanner and positioned thereon by plural pin attachment means associatedwith at least one of said rods, said glass sleeve material having asoftening point in excess of substantially 500 centigrade.

7. A color cathode ray tube according to claim 5 wherein said electrongun insulative shielding means are in the form of a plurality of curvedglass leaves whereof each has two opposed substantially arcuateend-oriented edges and two opposed substantially straight side-orientededges, said side edges being adjacently positioned in a lateralrelationship to collectively form a peripheral encompassment of saidelectron gun structure, each of said leaves being attached to anindividual of said support rods, the material of said glass leaveshaving a softening point in excess of substantially 500 centigrade.

8. A color cathode ray tube according to claim 5 wherein the compositionof said electron gun insulative shielding glass contains an x-radiationabsorptive material in the form of at least one metallic compoundselected from the group consisting essentially of lead,

barium and strontium.

1. An improved electron gun structure for use in a color cathode raytube having an envelope formed of a neck portion, a funnel portion and aface panel portion whereupon a cathodoluminescent screen is disposed,said electron gun structure being constructed for subsequent orientationwithin the neck portion of said envelope and comprising: a plurality oflongitudinal arrangements of associated electrodes related in a mannerto subsequently provide for generating, forming and focusing a pluralityof beams of electrons toward said cathodoluminescent screen; a pluralityof glass support rods spatially oriented peripheral to said electrodearrangements to provide support and affixed positioning for said relatedelectrodes in said gun structure; a common magnetic convergence assemblycontiguous to and extending forward of the terminal electrodes of saidgun structure, and having resilient means peripherally associatedtherewith to effect the subsequent centering of said electron gunstructure in the neck portion of said envelope; and insulative glassshielding means arranged in a substantially encompassing manner aboutsaid supported electrode arrangements, said shielding being dimensionedto be spaced from the interior surface of said envelope neck portionwhen said gun is inserted therein to provide shielding for saidelectrodes, said glass shielding means being positioned and retained incontiguous bonded relationship to at least one of said support rods insaid gun structure, said shielding being oriented immediately to therear of said convergence assembly.
 2. An electron gun structureaccording to claim 1 wherein said insulative shielding means is fittedlongitudinally over the glass support rods and positioned by plural pinattachment means associated with at least one of said rods.
 3. Anelectron gun structure for use in a color cathode ray tube according toclaim 1 wherein said insulative shielding means are in the form of aplurality of curved glass leaves whereof each has two opposedsubstantially arcuate end oriented edges and two opposed substantiallystraight side oriented edges, said side edges being adjacentlypositioned in a lateral relationship to collectively form a peripheralencompassment of the plural beam electron gun structure, each of saidleaves being attached to an individual of said support rods.
 4. Anelectron gun structure for a color cathode ray tube according to claim 1wherein the composition of said insulative shielding glass contains anx-radiation absorptive material in the form of at least one metalliccompound selected from the group consisting essentially of lead, bariumand strontium.
 5. A plural beam color cathode ray tube comprising: anenvelope having face panel, funnel and neck portions; a patternedcathodoluminescent screen disposed on the interior surface of said facepanel; a plural beam electron gun structure located within said envelopeneck portion in a manner to project a plurality of electron beams towardsaid patterned screen, said gun structure being formed of a plurality ofsequential arrangements of associated electrodes positionally related byseveral spatially oriented longitudinal glass support rods; a commonmagnetic convergence assembly contiguous to and extended forward of theterminal electrodes of said gun structure and having resilient meansperipherally associated therewith to center said electron gun structurein the neck portion of said envelope; and insulative glass shieldingmeans arranged in a substantially encompassing manner about saidelectron gun structure and spaced from the interior surface of saidenvelope neck portion to provide shielding for said electrodes, saidshielding means being positioned and retained in bonded attachment tosaid gun structure support rods immediately to the rear of saidconvergence assembly.
 6. A color cathode ray tube according to claim 5wherein said electron gun shielding means is in the form of a sleevefitted longitudinally over the glass support rods of said electron gunstructure in a contiguous manner and positioned thereon by plural pinattachment means associated with at least one of said rods, said glasssleeve material having a softening point in excess of substantially 500*centigrade.
 7. A color cathode ray tube according to claim 5 whereinsaid electron gun insulative shielding means are in the form of aplurality of curved glass leaves whereof each has two opposedsubstantially arcuate end-oriented edges and two opposed substantiallystraight side-oriented edges, said side edges being adjacentlypositioned in a lateral relationship to collectively form a peripheralencompassment of said electron gun structure, each of said leaves beingattached to an individual of said support rods, the material of saidglass leaves having a softening point in excess of substantially 500*centigrade.
 8. A color cathode ray tube according to claim 5 wherein thecomposition of said electron gun insulative shielding glass contains anx-radiation absorptive material in the form of at least one metalliccompound selected from the group consisting essentially of lead, bariumand strontium.